Co-axial discharges



Nov. 22, 1960 J. s. LUCE ET AL 2,961,558

CO-AXIAL DISCHARGES Filed Jan. 29, 1959 5 Sheets-Sheet l 18 GAS SOURCE GAS SOURCE GAS SOURCE R. F. VOLTAGE SOURCE R. F. VOLTAGE SOURCE INVENTORS John S. Luce 8: BY Lloyd P. Smifh flM Q-W ATTORNEY Nov. 22, 1960 J, 3 L CE ET AL 2,961,558

co-AxIAL DI SCHARGES Filed Jan. 29, 1959 3 Sheets-Sheet 2- GAS /80 SOURCE 99 SOURCE 101 INVENTORS John S. Luce '8 BY Lloyd P. Smifh Fig. 4a ATTORNEY Nov. 22, 1960 J. s. LUCE E L CO-AXIAL DISCHARGES 5 Sheets-Sheet 3 Filed Jan. 29, 1959 INVENTORS. John S. Luce 8 BY Lloyd P. Smifh ATTORNEY United States Patent 2,961,558 do-AxiAL ms'cnhnorz's John S. Luce, Oak Ridge, Tenn, and Lloyd P. Smith", North Andover, Mass., as'signors to'ithe United States of Americajas represented by the United States Atomic Energy Commission Filed Jan. 24,1959, set. *Nb. new 15 Claims. e1. sis-:63

energetic particles, stich 'lo'ss would prevent the transfer orenergytp the gas iii the chamber. Alsb-,fis6iiie attire injected particles are lost b cemsida's with iivalls' and solidelectrodes. v

With a khow'le'dge er rue fact that injected energetic particles "Will be lost by "fetii rriin g lo the "some I n silch injection and/or by collisions with walls andfsohd *elec trodes, it"is aprimziry object of this invntioh"to rovide co 'artial arc dischaig cs 'which will provi d'efa in aris of hea ing assa a idw srssure'deiitennm r tiitiurn gas to temperatures high enough to produce useful nuclear c nteens by a e1ertiag deiit'eiihi'n er tritium ions in the region etweeii'the-ar'essb that they'att'ain sufiiciently high energies to be useful, and thence communicate this energy to other diiteions or hit h sin an efficient manher, or to accumulate e'noiigh ions inthe region so that trapping woilldresult from ion ijon collisions.

It is aiiother object of this invention to provide coaxialg arcdischarge's in a magne c fieldaiidwith a potentialgradient -establish betw n the discharges to accelerate lofts and electrons acrossthe field, to thereby 'efie'cttrappiiig of a portion of sai'd'i'ons. 7

H is still another object of this Invention to provide a dev for produciiig co-aid ischarges in which all phys cal ectrodes inithe operating volume are replaced with arc dis arg es which act as felectrod'es.

and oth'e'r objects 'aiid advantages will become a arerit frbrh "a considerationof the following detailed specification'and 'tiiefaccorhpa'riying drawings, wherein: M Fig. 1'shows a cross sectional view of co-axial arc discharges in a mirror type nia'ch'ine,

Fig. 2 shows "a sectional view on the line 2 2 of Fig. l, withtheoht'er "are being positive with respect to Fig. 3 fshows'a sectional viewof a hollow central are which can be substituted'for the central arc of Fig. 1, t

% Fig.4 shows a sectional view on line 22 of Fig. 1 when the arc of Fig. 3 is substituted for the centr'alarc ofhijg. l, and with the same polarity across the arcs asinFigga j Fig. 5 shows a rass-sec iona view of a device in which a sj'olid cylinder is 'iised' to enclose the central are discharge, V A l ,t Fi'g. s -"shaw s "a transactionalyiew'oa the IiireM t otlFig. 5', k j M i Fig. 7 shows across-sectional view on the line 2:4

of Fig. 1 where a solid electrode is substituted for the central arc in Fig. 1,

Fig. 8 shows a cross-sectional view on the line '2- 2 of Fig. 1, with the inner are being positive with respect to the outer arc, and

Fig. 9 is a cross-sectional view on the line 2-2 of Fig. 1 when the arc of Fig. 3 is substituted for thecentral arc of Fig. l, with the inner arc being positive with respect to the outer are.

The objects stated above have been achieved in the present invention by providing a strong, axial magnetic field and an axially aligned 'outei cylindri al deuterium or tritium arc and 'an ihner cylindrical or solid deuterium or tritium are so operated that the potential of the two arcs are opposite in sign. When the arcs are maintained at a high potential difference, electrons will diffuse to the more positive are from the negative arc and positive ions will diffuse from the more positive are to the negative are. Due to the very small electron orbits in the magiietic field, they must make many collisions before they arrive at the more positive arc and consequently the resistance to how of electronswill be great. 'An ion leaving t mor'e positive arc will have substantially zero energy. When it attains its maximum energy during acceleration across the 'rriagiiet'ic field, it will return to the more positive'arc'unless it makes a collision in its trajectory. If the ion doe's not make a collision in its trajectory,-then when itreturns to the more positive are where it originated, it will again have zero energy and can start a new trajectory; thus no energy is lost from the power supply until a collision with another ion or atom takes place. If a collision does take place, the ion then travels on a trajectory, on the average, that would allow it to be accelerated toward the 'negativearc or be trapped in the region between thearcs. When and if the ion reaches the negative are it does notlose energy except by making a useful collision, so that the energy of the ion thus accelerated is not lost by conversion to useless heat energy at a solid electrode.

The use of a strong mirror magnetic field and themaxial arcs permits the plasma to be contained,'whilethe ions are accelerated to high energies.

v Either of the'con'centric arcsmaybe made more positive'than the other and only the more positive arc need be a gas are to provide a source of positive ions for the device. In addition, a solid electrode may be substituted for either the inner or outerar'c with the remaining a'rc held at a positive potential with respect to the solid electrode. In all possible configurations, th'eoperation is the same; that is, positive'ions will difiuse across the magnetic field from the positive gas ar'cto a negative solid electrode or are in the *same manner as indicated above. The are discharges employed in the various modifications are considered to be electrodes since they perform'the same function as electrodes with the exception that no energy is lost fromthe' system by ions'striking the discharges.

Referring now to Fig. l which illustrates one embodiment in which the principles of this invention may be carried out,a" centrally bored cathode 1 is mounted to the chamber wall 5 by an insulator 3, for example. An anodeelectrode 2 is mounted to the chamber wall 5 by'an insulator 4, for example. Deuterium or tritium gas is fed froma'source 18, through tube 17 and hole 16 in cathode 1 to the face thereof. In some cases, it may be desired't'o feed gas to the face of the anode in a manner'siririlar to that for cathode 1. A pair of magnetic mirror co'ils 19 and '20 are disposed adjacent to the cathode and anode respectively as shown, and a plurality of magnetic solenoicl coils 21 are disposed in end-to-end relation between the mirror coils '19 and 20. The mirror coils and sole,

noid coils provide a containing magnetic field as illustrated by the dashed lines within the container 5 as shown. The chambers 36 and 62 are connected to vacuum pumps through the openings 25 and 26, respectively. The inner chamber 35 is connected to a'vacu'um pump by the opening 27. A variable source of DC. potential, such as a multi-cell, variable-tap battery 5%), is connected at one side to cathode 1 by a lead-51 and lead 52, and is connected at its other side to anode 2 by a lead 53, switch 54, lead 55, and lead 56. A source of RF. voltage 57, such as used in aconventional welding system, is connected at one side to cathode 1 by a lead 58, and lead 52, and is connected at its other side to anode 2 by lead 59, switch 60, lead 61, and lead56. The energetic arc discharge 34 may be initiated and sustained between the cathode 1 and anode 2 in a manner similar to that disclosed, for Fig. 1 of the application of Persa R. Bell and John S. Luce, Serial No. 750,834,'filed July 24, 1958 now Patent No. 2,920,235, issued January 5, 1960. p

The are discharge 33 may be a refiux-type discharge operating on the Phillips ionization gauge principle. It may also be a DC. are or a discharge similar to the discharge 34, or othersuitable discharge if desired. The apparatus for providing the reflux discharge 33 will now be described. A cylindrical cathode 6 is connected through an opening 10 to an area 31 of the gas chamber 8. The chamber 8 is mounted by an insulator 29 to the coil 19 housing. Deuterium or tritium gas is fed from a source 14, and through a tube 12 to the interior of annular chamber 8. A cylindrical cathode 7 is connected through'an opening 11 to an area 32 of the gas chamber 9, The chamber 9 is mounted by an insulator 30 to the housing around coil 20. Deuterium or tritium gas is fed from a source 15, and through tube 13 to the interior of annular chamber 9. A cylindrical anode 22 is mounted by insulators 23 and 24 to the housing on some of the coils 21. The anode 22 may be in the shape of a simple ring if desired. A source of variable DC. potential 37 such as a variable-tap, multi-cell battery or D.C. genergator, is connected at one side to the anode 22' by lead 38, andat its other side to cathode 6 by lead 39, switch 40, lead 41, lead 48, and lead 47, and to cathode 7 by lead 39, switch 40, lead 41, and lead 42. An R.F. voltage source 43, such as used in a conventional welding system, is connected at one side to anode 22 by a lead 49, and is connected at its other side to cathode 6 by a lead 44, switch 45, lead 46, and lead 47, and to cathode 7 by lead .44, switch45, lead 46, lead 48, and lead 42. The refluxtype discharge 33 maybe initiated and sustained in a manner similar to that disclosed for Fig. 3 of the application of John S. Luce, Serial No. 748,771, filed July 15, 1958, now Patent No. 2,927,232, issued March 1, 1960.

The electrodes 1 and 2 may be cooled by any suitable means such as cooling tubes 107 and 108 mounted in jackets 63 and 64, respectively, and disposed around the electrodes. Also, annular baflles 111 and 112 are mounted on members 110 and 109, respectively, and are provided adjacent to each of the cathode 1 and anode 2 electrodes, respectively, in a manner similar to that shown inthe aforementioned application. In addition, annular bafiles and cooling coils may be provided for the electrodes 6 and 7 for the outer are 33.

In one operation of the apparatus of Fig. 1 at startup, gas is fed from source 18, through tube 17, and through hole 16 in cathode 1 to the cathode face. Gas is also fed from source 14, and through tube 12 to interior of chamber 8, and then through opening 10 to the face of cathode 6, and gas is' fed from source 15, and through tube 13 to the interior of chamber 9, and then through opening 11 to the face of cathode 7. When the pressure at the faces of all the cathodes reaches a value of 3 l0- mm. Hg, an RF. voltage source 57 and a DC.

source 50 are connected across the electrodes 1, 2, and

an R.F. voltage source 43 and a DC. source 37 are connected across the electrodes 6, 7 and 22. After the arcs 33 and 34 are initiated, the R.F. voltage sources are disconnected. The pressure in chamber 35 is then gradually reduced until it reaches a value of approximately 5x10- mm. Hg, or lower. The pressures in outer chambers 36 and 62 are maintained at a value of approximately 3 X10 mm. Hg, or lower. The arcs may be initiated at startup with a pressure lower than 3 x10" mm. Hg pro vided the RF. voltage sources and the operating potentials are correspondingly increased. When a DC. gas arc is used for the outer arc, it may be initiated and sustained in a manner similar to arc 34. Under these conditions the anode 22 would not be required and the cathode 7 would then be used as an anode and the potentials-across the electrodes would then be connected in the same manner as for electrodes 1 and 2 for the inner arc.

There are several other conventional methods for helping to initiate an arc discharge between the electrodes other than those specified above, such as applying a very high starting potential between the electrodes, heating the electrodes until they are completely outgassed and then applying a high starting potential between the electrodes, or by providing an auxiliary electrode adjacent to the cathode and momentarily touching the cathode with said auxiliary electrode while at the same time applying a voltage between the cathode and auxiliary electrode until an arc is struck between them and then separating said electrodes while applying an are potential between the cathode and anode, and then removing the auxiliary electrode. 7

During all stages of operation of the apparatus of Fig. l, a magnetic field strength of a selected value, for example 3000 to 6000 gauss, is maintained by the coils 21. The field strengths of the mirror coils 19 and 20 are set at a value higher than that produced by solenoid coils 21 so as to provide the magnetic mirror regions at each end of the device.

In the device of Fig. 1, the outer are 33 may be positive with respect to the inner are which may be negative. Whenthe arcs are maintained at a high potential difference, 20-50 kv., for example, electrons will tend to diffuse from the inner arc to the outer arc and ions'from the outer arc to the inner are as discussed above. If the charged particle does not have a collision in its trajectory when it leaves the outer arc, it returns to the outer arc and a new trajectory will begin, as shown in Fig. 2. When ions do suffer a collision, they may see a higher electric field and be accelerated to higher energy and as they make more collisions, they will eventually reach the inner are. Thus a strong plasma is built up that is essentially a concentric rotating ring of ions surrounding the inner arc, and circulating currents are set up in this ring.

If desired, the polarity of the arcs of Fig. 1 may be reversed so that the outer arc 33 may be negative with respect to the inner are which then may be positive. In this case the electrons will tend to diffuse from the outer arc to the inner arc, and the ions from the inner arc to the outer arc. Fig. 8 shows a cross-sectional view .of Fig. 1 andthe ion paths when the polarity of the arcs is thus reversed. In both cases, the negative arc need not be a gas are butmay be a conventional D.C. arc.

The use of co-axial arc discharges for confining an ionized plasma between said discharges has the advantage. of preventing impurities from the walls of the device from entering the plasma area because of the arc barrier set up by the cylindrical outer arc.

The are discharge 34 of Fig. 1 need not be a solid are but may be hollow. Fig. 3 shows the electrode structure for producing a hollow inner are that can be substituted for the inner arc of Fig. 1. This hollow arc may be in itiated and sustained in a manner similar to that disclosed for Fig. lot the aforementioned Luce application. The are 68 of Fig. 3 is initiated between a cathode 65 and an anode 66. Gas is fed through a tube 67 to the interior of the cathodewhich is a hollow elongated electrode. The

eate;or.gas-teed=w the cathode is r'e'g'ulated'so that a sheath forms within the cathode where substantially complete space charge neutralization and ionization of the gas takes place before it leaves the cathode. In some cases, it may be desirable to feed gas toth'e face of the anode 66 'by'ineans not'shown. When the are '68 of Fig. 3 issubs'tituted for the arc '34of"Fig. '1,'i'oriswill be accelerated at high energy from the outerpcisitive are 33 and will enter a 'field free" ('eli'z'trds'tatic) [region within the innermost negative arc and retain their high "energy, as clearly 'shown in the ress-seesaw 'viewof Fig. 4 which shows" the concentric hollow arcs" d 'theion paths. In this "arrangement, afiplasrna of ene etic iohs will form regardless of wherethe'a'r'iotie and cathode sheaths farm. Unlike other cases, the ions are-accelerated tofull nrg'y independently of the pressure.

If desired, the polarity of the arcs as shown in Fig. 4 may be 'reversed so thatthe arc-33 is negativewith respect to the inner are 68 which is positive. Fig. 9 shows a crossse'ctioiial view'or the arcs and the'ion path's with such a reverse polarity. The 'ions will pass through the outer are 33 into a field-free (electrostatic) regionsurroundi'ng theouter are. It should be noted th-atin this case, the ions also are accelerated from the more positive are. In addition, the more positive are, whether it be the center or outer arc, should be a gas fed arc, and the other negative arc may then either be a gas fed are or a conventional D.C. arc.

If desired, the outer are 33 of Fig. 1 may be replaced with a cylindrical member. Fig. 5 shows such an arrangement. In Fig. 5 the said cylindrical member is held at a negative potential while the central arc is maintained at a positive potential with respect to said member. Fig. 6 shows a cross-sectional view of Fig. 5 with such polarity connections, and the corresponding ion paths. The paths of the electrons and ions are reversed to what they are in the device of Fig. 1. Otherwise, the operation of the device is the same as for Fig. 1. Since the device of Fig. 5 employs the use of a solid electrode, the energetic ions are lost when they finally strike the outer cylinder. However,

it does operate in a similar manner since there is a potential gradient between the arc and the concentric cylinder surrounding the arc.

In Fig. 5, a cathode 70 is mounted by an sulator 72 to be container wall 74, and an anode 71 is mounted by an insulator 73 to the wall 74. Magnetic mirror coils 75 and 76 are disposed adjacent to the cathode 70 and anode 71, respectively. Solenoid coils 77 are disposed in end-to end relation between the mirror coils 75 and 76. The mirror coils and solenoid coils provide the containing magnetic field for the device as shown by the dashed lines within the container. A hollow cylindrical member 81 is mounted by insulators 82 and 83 to the housing on some of the coils '77. A simple ring may be used instead of the cylindrical member 81, if desired. Cooling coils for the electrodes 70 and 71 and battles mounted adjacent the electrodes 70 and 71 may be provided, if desired, in a manner similar to that set forth for Fig. 1 above. The chamber 104 is evacuated by a vacuum pump connected to member 87 and through opening 86. The chambers 105 and 106 are evacuated by vacuum pumps connected to openings 84 and 85, respectively, in the outside wall 74. A source of gas 80 is connected by tube 79 and bore 78 in cathode 70 to the face of said cathode. A source of DC. potential, such as a variable-tap, multi-cell battery 92 or DC. generator, is connected at one side to cathode 70 by lead 93, and lead 94, and at its other side to anode 71 by lead 95, switch 96, lead 97, and lead 38. A source of RF.

voltage 99, such as used in a conventional welding system, is connected at one side to cathode 70 by lead 100, and lead 94, and at its other side to anode 71 by lead 101, switch 102, lead 103, and lead 98. The cylindrical member 81 is connected to one side of battery 89 by a lead 90, and the other side of battery 89 is grounded. The

are discharge 88 between c'athbd 70 and 'a'n't'jd'e 71 may be initiated, and sustained the same as the discharge-34 of Fig. ,1 The are discharge, 6-8 of Fig. 3 may be 'substitute'd for the discharge '88 of Fig. '5 if desired. I

If desired, a central electrode 1 10'may besub stituted for the centr'alarc '34of Fig. Land the outer'arc discharge 33 wouldythen be held at a positive potential with respect to the central element. In such an arrangement the positive ions rre'injthsouterarcss would be "accelerated -'tc'iward the central electrode I10. Fig. 7 shows a cross-secti'o'rial'viewof'such anarrahg'ment with the cbrr ""end n'gibn paths, I I

The are discharges set'foi'th in the instant disclosure are also useful as a means for providing a source of energetic io fahd al soasfdi ssocia'tion mechanisms for injected 'energetic molecularioris in a manner set forth in the 'applieatienisrioits's. Luce, Serial No. 728,754, filed April 15,1958. I M I This. invention has been described byway of illustration rather than limitation and it should b appare t that the invention is equally applicable in fields other than those described. I

1. A method for forming an eh'erge'tic ion plasma comprising the steps of establishing a magnetic field oriented along the axis of an evacuated container, establishing magnetic mirror fields at each end of said container and oriented along said axis, initiating and sustaining a gas fed arc discharge coaxial with said axis, and establishing and maintaining a radial potential gradient normal to the surface of said arc discharge to accelerate ions therefrom and attract electrons thereto.

2. A method for forming an energetic ion plasma comprising the steps of establishing a magnetic field oriented along the axis of an evacuated container, establishing magnetic mirror fields at each end of said container and oriented along said axis, intiating and sustaining a first arc discharge coaxial with said axis, initiating and sustaining a second cylindrical arc discharge coaxial with said first discharge and spaced apart therefrom to provide an annular space between said discharges, at least one of said discharges being a gas fed discharge, and establishing and maintaining an electrical potential gradient between said discharges, whereby charged particles including both ions and electrons are accelerated between the discharges thereby building up and trapping a plasma of energetic particles in said annular space.

3. The method set forth in claim 2, wherein the cylindrical arc discharge is a gas fed arc discharge and wherein said electrical potential gradient is established in such direction that ions are accelerated from and electrons are accelerated toward said cylindrical arc discharge.

4. The method set forth in claim 2, wherein said first arc discharge is a gas fed arc discharge and wherein said electrical potential gradient is established in such direction that ions are accelerated from and electrons are accelerated toward said first arc discharge.

5. A device for forming energetic ions comprising a container, means for evacuating said container, means providing a containing magnetic field within said container and oriented along the axis of said container, means providing a magnetic mirror field at each end of said container and oriented along said axis, a first electrode disposed along said axis, a second cylindrical electrode coaxial with said first electrode with an annular space between said electrodes, at least one of said electrodes being a gas fed arc discharge, and means connected between said electrodes for establishing a large potential gradient therebetween, whereby charged particles including both ions and electrons are accelerated into said space between the electrodes, thereby building up and trapping a plasma of energetic particles.

6. The device set forth in claim 5, wherein the axial electrode is the gas fed arc discharge, the cylindrical electrode is a DC. are discharge, and the axial electrode is held at a positive potential with respect to the cylindrical electrode.

7; The device set forth in claim 5, wherein the cylindrical electrode is the gas fed arc discharge, the axial electrode is a'D.C. arc discharge, and the cylindrical electrode is held at a positive potential with respect to the axial electrode.

8. The device set forth in'claim 5, wherein both electrodes are gas fed arc discharges.

9. The device set forth in claim 5, wherein the axial electrode'is a hollow gas fed are discharge, the cylindrical electrode is the gas fed arc discharge, and the axial electrode is. held at a positive potential with respect to the cylindrical electrode.

10. The device set forth in claim 5, wherein the axial electrode is a hollow gas fed' arc discharge, the cylindrical electrode is the gas fed arc discharge, and the cylindrical electrode is held at a positive potential with respect to the axial electrode.

'11. The device set forth in claim 5, wherein the gas fed arc discharge electrode is the axial electrode, the cylindrical electrode is a solid electrode, and the axial electrode is held at a positive potential with respect to the solid cylindrical electrode,

8 12. The device set forth in claim 5, wherein the gas fed arc discharge electrode is the cylindrical electrode, the axial electrode is a solid electrode, and the cylin drical electrode is held at a positive potential with respect to the solid axial electrode. v

13. The device set forth in claim 5, wherein the gas fed to the arc discharge electrode is a mixture of deuterium and tritium.

14. The device set forth in claim 5, wherein the gas fed to the arc discharge electrode is tritium.

15. The device set forth in claim 5, wherein the axial electrode is the gas fed arc discharge and is hollow, the cylindrical electrode is a D0. are discharge, and the axial electrode is held at a positive potential with respect to the cylindrical electrode.

References Cited in the file of this patent Atomic Industry Reporter, News and Analysis, Official Text Section, 1958, filing No. TK 9001 A7, issue of January 29, 1958, pages 54:5 54:1l.

Project Sherwood, Bishop, Addison-Wesley Press, Reading, Mass., 1958, pages 67-69. 

